ERW Steel Pipe Microstructure for Low Yield Ratio and Toughness
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Solution Overview
Problem
Existing electric resistance welded steel pipes face challenges in achieving both low yield ratio and high toughness, particularly in thick-walled pipes, due to work hardening during production, which is exacerbated by increased wall thickness.
Innovation Solution
The steel pipes are manufactured with a bcc phase volume fraction greater than or equal to 80%, average grain size less than or equal to 15.0 μm, and an A value of 0.55 or greater and 0.85 or less, controlled through specific hot rolling, cooling, and rolling conditions, to inhibit dislocation entanglement and promote mobile dislocations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If cold roll forming is performed to achieve high productivity and dimensional accuracy, then productivity and dimensional accuracy are improved, but work hardening occurs and yield ratio increases
Solution Approach 1:
The invention performs preliminary action by optimizing the microstructure before the cold roll forming process. Through controlled hot rolling and cooling to achieve specific microstructural parameters (bcc phase volume fraction ≥80%, average grain size ≤15.0 μm, A value 0.55-0.85), the material is prepared in advance to resist work hardening during subsequent cold forming, thereby maintaining yield ratio ≤90% while preserving the productivity and dimensional accuracy benefits of continuous cold roll forming production
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach results in a steel pipe with a yield ratio less than or equal to 90% and Charpy absorbed energy greater than or equal to 100 J, suitable for large structures requiring high toughness and seismic resistance.
Implementation Method 1
steel microstructures at a wall-thickness-wise middle of a base metal zone are steel microstructures in which a bcc phase is present in a volume fraction greater than or equal to 80%, an average grain size is less than or equal to 15.0 μm, and an A value is 0.55 or greater and 0.85 or less
Implementation Method 2
A hot rolled steel sheet (hot rolled steel strip) coiled in a coil form is subjected to cold roll forming while the hot rolled steel sheet is continuously uncoiled, to form a cylindrical open pipe
Implementation Method 3
the hot rolled steel sheet is subjected to cold roll forming... to form a cylindrical open pipe
Implementation Method 4
electric resistance welding in which pipe-circumferential butt portions thereof are melted by high-frequency electrical resistance heating and pressure-welded with upsetting caused by squeeze rolls
Implementation Method 5
electric resistance welding in which pipe-circumferential butt portions thereof are melted by high-frequency electrical resistance heating and pressure-welded
Implementation Method 6
the resultant is subjected to diameter reduction performed by sizing rolls, to have a predetermined outside diameter
Data Source
AI summary
An electric resistance welded steel pipe and a method for manufacturing the same are provided. The present invention relates to an electric resistance welded steel pipe including a base metal zone and a weld. In the electric resistance welded steel pipe, steel microstructures at a wall-thickness-wise middle of the base metal zone are steel microstructures in which a bcc phase is present in a volume fraction greater than or equal to 80%, an average grain size is less than or equal to 15.0 μm, and an A value, defined by a predetermined equation, is 0.55 or greater and 0.85 or less; a yield ratio in a pipe axis direction is less than or equal to 90%; and a Charpy absorbed energy at −40° C. of the base metal zone is greater than or equal to 100 J.